Influenza A viruses cause epidemics and pandemics in human populations, inflicting enormous suffering and economical loss. Currently, two distinct strategies - vaccines and low molecular weight drugs - are utilized to control the spread of influenza. Vaccination offers limited protection and is hampered by logistic challenges: accurate prediction of future circulating strains and production of sufficient quantities of vaccine for large populations in a short time. Four antiviral drugs have been approved in the United States for the treatment and prophylaxis of influenza. Two of them, amantadine and rimantadine, inhibit the viral M2 ion channel protein, and other two, zanamivir and oseltamivir, inhibit the viral neuraminidase activity. Besides the limited therapeutic window, side effects and high costs, most circulating viruses are already resistant to the two M2 inhibitors and development of resistance to the neuraminidase inhibitors is inevitable if they are widely used. The need to develop novel influenza therapeutics that can prevent viral resistance or significantly reduce its incidence is urgent and compelling. We have developed bi-functional polymer-attached zanamivir and sialic acid (a competitive inhibitor of viral hemagglutinin) based on (i) the principle of combination therapy of simultaneously interfering with two distinct targets on the virus and (ii) the observation that polymeric forms of a competitive inhibitor are much more potent than the monomeric counterpart. In preliminary studies, we have shown that the bi-functional polymer-attached inhibitor is much more potent than monomeric inhibitors or mono-functional polymer-attached inhibitors. In this application, we propose to 1) enhance the antiviral activity of the polymer-attached inhibitors by systematically optimize the level of conjugation and the type and size of the polymer backbone and the linker, 2) systematically evaluate the potency of the polymer-attached inhibitors in appropriate human target cells and animal models to a broad range of influenza virus isolates, including the highly pathogenic avian viruses H5N1 and H7N7, 3) to quantitatively assess the ability of the polymer-attached inhibitors to reduce viral resistance, and 4) to elucidate the antiviral mechanisms of the polymer-attached inhibitors so as to further rationally improve their antiviral activities. It is anticipated that the proposed research will (i) yield one or more highly potent, optimized polymer-attached inhibitor(s) for future clinical development and (ii) provide a new paradigm of drug development for overcoming microbial drug resistance